Improve messaging and dashboard reliability

tests/recipient-deduplicator.test.ts

@@ -0,0 +1,29 @@
+import { describe, expect, it, vi } from 'vitest';
+import { RecipientDeduplicator } from '../src/services/recipient-deduplicator.js';
+
+describe('RecipientDeduplicator', () => {
+  it('reserves a recipient once across username casing variants', () => {
+    const history = { hasSentTo: vi.fn(() => false) };
+    const deduplicator = new RecipientDeduplicator(history);
+
+    expect(deduplicator.tryReserve('Some_User')).toBe(true);
+    expect(deduplicator.hasSentTo('some_user')).toBe(true);
+    expect(deduplicator.tryReserve('SOME_USER')).toBe(false);
+  });
+
+  it('rejects recipients found in persisted cross-account history', () => {
+    const history = { hasSentTo: vi.fn((recipient: string) => recipient === 'contacted') };
+    const deduplicator = new RecipientDeduplicator(history);
+
+    expect(deduplicator.tryReserve('contacted')).toBe(false);
+    expect(deduplicator.tryReserve('new-user')).toBe(true);
+  });
+
+  it('allows another account to retry after a failed send releases its reservation', () => {
+    const deduplicator = new RecipientDeduplicator({ hasSentTo: () => false });
+
+    expect(deduplicator.tryReserve('retry-user')).toBe(true);
+    deduplicator.release('RETRY-USER');
+    expect(deduplicator.tryReserve('retry-user')).toBe(true);
+  });
+});